One method that has been employed for illuminating scattering mode type liquid crystal display devices has been to back the display with an "optical louver" and to mount a light box behind the optical louver. The optical louver, which may be for instance of the type marketed by the 3M Company, allows light to pass through it within a narrow angular range which lies entirely outside the viewing angle range of the display device. Thus the observer cannot directly see the illuminating light, but only that which is scattered by scattering regions of the liquid crystal layer of the display device.
A drawback of this optical louver approach to the provision of illumination for the display is that it is generally found that, unless some form of lighting array is provided, the light box needs to be quite deep in order to secure adequately even illumination across the whole display area. Under these circumstances any advantage of the display cell thinness, as compared for instance with a conventional CRT, is effectively wasted.